Stiffening structures for stiffening long flat panels often use a ladder-type configuration secured to the panels to provide rigidity and support to the panels. Applications of such stiffening structures include fuselage, winglets, and other wing-like parts used in the commercial and military aircraft industries. FIG. 1 illustrates a typical ladder-type structure 10 secured to a wing skin panel 16. A first spar 12 and a second spar 14 extend along a length of the wing skin panel 16 from a base end 20 to a tip end 22. A third spar 18 lies between the first spar 12 and the second spar 14 and extends along a portion of the first spar 12 and the second spar 14 from the base end 20. A number of ribs 24 couple the first spar 12 to the third spar 18 and the third spar to the second spar 14. The spars and the ribs typically are of I-beam or C-beam configuration. Accordingly, to further stiffen the structure 10, a core 26 is embedded in the wing skin panel in the area of the ribs. The core is typically made of a honeycomb resin material.
While these ladder-type configurations stiffen and strengthen long structures such as fuselage- or wing-type structures, they display several drawbacks. The members of the ladder-type configuration, such as ribs and spars, are typically attached to each other using fixing devices, for example, screws, bolts, or nuts. Consequently, manufacturing the ladder-type configurations using such fixing mechanisms is quite time consuming and expensive. In addition, the members and the fixing devices usually are made of metal that adds weight to the stiffening structures. Further, the ladder-type configurations provide only limited stiffening support, thus requiring that the stiffening structures use additional stiffening mechanisms, such as core 26.
Accordingly, it is desirable to provide stiffening structures made of rigid but lightweight composite material. In addition, it is desirable to provide stiffening structures that are time- and cost-efficient to manufacture. It also is desirable to provide methods for manufacturing such stiffening structures. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.